JPH066218A - A/d converter with temperature compensating function - Google Patents

Abstract

PURPOSE:To provide an A/D converter having a temperature compensating function which has no malfunction and the low production cost and can reduce the A/D conversion error caused by the temperature change down to an ideal level by using simple circuit constitution and a prescribed arithmetic processing. CONSTITUTION:An A/D converter 1 consists of an A/D converting circuit 2 which has at least an input/output terminal and a control means 3 which controls the circuit 2. The means 3 has a temperature compensating function which applies the output correction together with the prescribed correction value to the digital signal which is converted from the analog signal inputted to an input terminal IN of the circuit 2 through the circuit 2 and outputted from an output terminal OUT and corrects the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog / digital converter, and more particularly to an analog / digital converter capable of compensating an A / D conversion value in response to a change in environmental temperature. It is about.

[0002]

2. Description of the Related Art Conventionally, as a device for converting analog signal data into digital signal data, an analog / digital conversion device has been widely used in many fields including, for example, a successive approximation circuit. By the way, in such an analog / digital converter, ideally, it is preferable that the output signal data have a linear relationship with the input signal data, but the A / D converter originally concerned has It has a unique characteristic with respect to temperature, and is therefore affected by the ambient temperature in which the A / D converter is used, and the conversion data inevitably contains conversion errors related to the temperature during conversion. It will be a matter.

In other words, there is a certain tolerance between the analog / digital converter and the ideal or standard. For example, in a certain analog / digital converter, if an error within ± 2 LSB is guaranteed within the operating temperature range of -40 ° C to 100 ° C under the standard of 10-bit resolution, the operating voltage is 5V. ± 10 mV
It is required to keep the error within the error range.

FIG. 10 shows an error within ± 1 LSB within a temperature range of −40 ° C. to 120 ° C. under a standard of 10-bit resolution required by a predetermined system including an analog / digital conversion circuit. FIG. 6 is a diagram exemplifying a state in which the A / D conversion error in the A / D converter changes with a change in temperature when a request is made. The example in FIG.
It shows an ideal conversion error for the required standard.

Further, FIG. 11 shows that, in an analog / digital converter, a conversion error is satisfied with respect to a required standard from a temperature characteristic of the analog / digital converter circuit at a specific temperature. It shows the relationship that the required characteristics will not be satisfied when the requirement becomes severe. That is, in such an analog / digital conversion circuit, it is preferable that the converted output voltage with respect to the input voltage has a substantially linear relationship as shown in FIG. 12, and further, as shown in FIG. Therefore, it is preferable that the conversion error with respect to the ideal output value is as close as possible to ± 0.

However, in the prior art, since the peripheral circuit must be devised so that the temperature change does not affect the analog / digital conversion circuit, the circuit configuration becomes large, and miniaturization and high integration are not possible. There is a problem that it is unsuitable and that the manufacturing cost increases significantly.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art and to idealize the A / D conversion error due to temperature change by using a simple circuit configuration and predetermined arithmetic processing. The present invention provides an analog / digital converter having a temperature compensation function that can be manufactured at a low cost, with no malfunction, without malfunction.

[0008]

In order to achieve the above-mentioned object, the present invention adopts the technical constitution as described below. That is, an analog / digital conversion device having at least an analog / digital conversion circuit having an input / output terminal and a control means for controlling the analog / digital conversion circuit, wherein the control means includes the analog / digital conversion circuit. Has a temperature compensation function that has a function of performing output correction by adding a predetermined correction value to the digital signal that is output by being converted by the analog / digital conversion circuit analog/
It is a digital conversion device.

[0009]

Since the analog / digital converter having the temperature compensation function according to the present invention uses the basic technical configuration as described above, even if the ambient temperature in which the analog / digital converter is used changes. Is converted by the analog / digital conversion circuit by using a correction value related to a necessary temperature, which is obtained from a predetermined temperature characteristic specific to the analog / digital conversion circuit with respect to the temperature change. The digital signal value is corrected.

That is, according to the present invention, when the ambient temperature of the analog / digital conversion circuit changes due to the inherent temperature characteristic of the analog / digital conversion circuit in advance, the analog / digital conversion is performed. The circuit determines in advance how much conversion error should be included in the analog / digital conversion, and when the analog signal input to the analog / digital conversion circuit is converted by the analog / digital conversion circuit, the digital signal is converted. The above-mentioned correction value, for example, the correction voltage value is added to the signal value or subtracted from the digital signal value to compensate the conversion error,
This is to obtain an accurate digital conversion value.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of an analog / digital converter having a temperature compensation function according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram illustrating a specific example of an analog / digital converter having the temperature compensation function according to the present invention. In the figure, an analog / digital converter 2 having at least input / output terminals,
An analog / digital conversion device 1 having a control means 3 for controlling the analog / digital conversion circuit, wherein the control means 3 has an analog signal input to an input terminal IN of the analog / digital conversion circuit 2. Is converted by the analog / digital conversion circuit 2 and output from the output terminal OUT by adding a predetermined correction value to perform output correction. Device 1 is shown.

As the analog / digital conversion circuit 2 used in the analog / digital conversion device 1 having the temperature compensation function according to the present invention, any analog / digital conversion circuit generally used conventionally can be used. It is possible. Further, as the control means used in the present invention,
Any arithmetic processing circuit may be used as long as it has a function of controlling the conversion processing of the analog / digital conversion circuit. As shown in FIG. 1, the same substrate 4 as the analog / digital conversion circuit 2 is used. Alternatively, it may be formed as a circuit independent of the analog / digital conversion circuit 2, for example, a microcomputer or the like provided in the analog / digital conversion circuit 2. You can

Further, as the control means 3, a CPU 3'such as the central processing circuit may be used. The predetermined correction value in the control means 3 in the present invention means that when the environmental temperature in which the analog / digital conversion circuit 2 is used changes, the conversion value is converted by the unique temperature characteristic of the analog / digital conversion circuit. This is a value for compensating for such a conversion error because an error is generated.

As the correction, when the ambient temperature of the analog / digital conversion circuit changes from the inherent temperature characteristic of the analog / digital conversion circuit in advance, which of the analog / digital conversion circuits should be used? It is confirmed whether or not the analog / digital conversion is performed including a conversion error of a certain degree, and the conversion error corresponding to the value is stored as a correction value in an appropriate storage unit or the like, and the analog / digital conversion circuit The input analog signal is the analog /
When converted by the digital conversion circuit, the above-mentioned correction value, for example, the correction voltage value is added to the digital signal value or subtracted from the digital signal value to compensate for the conversion error and to obtain an accurate digital value. The conversion value is obtained.

In the first specific example of the present invention, the predetermined correction value uses a fixed value determined based on the inherent temperature characteristic of the analog / digital conversion circuit. That is, in this example, the temperature characteristic of the analog / digital conversion circuit used is measured in advance, and a conversion error (α), for example, as an average value occurs with respect to the temperature change. I ask.

Then, the conversion error (α) is stored in the memory circuit of the control means, and every time the input analog value is converted into a digital value, the conversion error (α) is converted into the conversion error (α). By adding the correction values, an accurate conversion value that compensates for the temperature change is output.
Of course, if the conversion error (α) is a negative value, it is needless to say that the subtraction is substantially performed by the addition operation.

FIG. 2 is a flow chart for executing the first concrete example of the present invention. In step (1) after start, the value PM obtained by digitally converting the input analog value is If it is A, in step (2), the conversion error (α) is added as a correction value to the conversion digital value A to obtain the conversion value PM.

In the second concrete example of the analog / digital converter 1 having the temperature compensation function according to the present invention,
The predetermined correction value is calculated by the analog / digital conversion circuit.
The value represented as a function of the temperature change determined based on the inherent temperature characteristic is adopted. That is, in this specific example, it is measured in advance how the conversion error (α) of the analog / digital conversion circuit changes according to the ambient temperature, and the correction relating to the conversion error of the analog / digital conversion circuit is performed. The value is grasped as a function having temperature as a variable, and the conversion error function is stored in the storage means of the control means.

On the other hand, an appropriate temperature sensor is provided near or inside the analog / digital conversion circuit,
The ambient temperature in which the analog / digital conversion circuit is used is constantly measured, the information is transmitted to the control means 3, and the temperature is calculated from the temperature information based on the correction value function of the conversion error stored in the storage means. The correction value corresponding to is selected and the digital value converted by using the correction value (α) when the control means converts the input analog signal into a digital value by the same method as in the first specific example. The correction is applied to.

FIG. 3 is a diagram for explaining a configuration example of an analog / digital conversion circuit in the case of executing the present concrete example. The analog / digital conversion circuit is composed of the analog / digital conversion circuit 2 and an appropriate control means 3. In the device 1, a temperature sensor 5 that is connected to the analog / digital conversion circuit 2 and detects the environmental temperature of the analog / digital conversion circuit.
Is provided.

The temperature sensor is not particularly limited, and may be a known temperature sensor, for example, one using a thermistor 6 as shown in FIG. 4, or as shown in FIG. It is also possible to use the diode 7. In any case, when the analog signal input to the input terminal IN is converted into a digital value in the analog / digital conversion circuit 2, a correction value corresponding to a conversion error that changes depending on the environmental temperature. (Α)
Is added to or subtracted from the digital value to correct the error of the digital conversion value.

The flow chart of the analog / digital conversion operation of the second specific example is substantially the same as that of FIG. 2, and differs from the specific example 1 only in that the correction value (α) is a function of temperature. Next, the third specific example of the analog / digital converter having the temperature compensation function according to the present invention will be described. The predetermined correction value used in this specific example is the above-mentioned first correction value. The analog / digital conversion circuit uses a fixed value determined based on the inherent temperature characteristic of the analog / digital conversion circuit as in the case of the above specific example. When the environmental temperature in which the conversion circuit is used deviates from a predetermined temperature range set in advance, output correction is performed using the correction value.

That is, in this example, the analog / digital conversion circuit 2 satisfies the required standard under a relatively normal temperature condition, but the temperature condition becomes high or low. Then, in a severe temperature environment, a predetermined conversion error (α) occurs between the ideal conversion and the actual conversion. Therefore, for example, the temperature is from -10 ℃ to +25 ℃
A temperature range such as that is set, and within the temperature range, a fixed correction value obtained from the temperature characteristic peculiar to the predetermined analog / digital conversion circuit is used. Although the conversion error is corrected, if the environmental temperature of the analog / digital conversion circuit 2 exceeds the above temperature range, for example, exceeds + 25 ° C. or drops to −10 ° C. or less, it is determined in advance. The conversion process is executed by using another conversion error value, that is, the correction value (α ′) or (α ″).

In the third specific example, in the predetermined temperature range, an average conversion error (α) is first obtained from the temperature characteristic of the analog / digital conversion circuit 2 and The conversion error (α) or (α ″) of the analog / digital conversion circuit 2 when the temperature range is deviated is separately provided, and the conversion error (α) or (α ″) is set according to the range of the environmental temperature of the analog / digital conversion circuit 2. The correction value is switched and used.

FIG. 6 is a block diagram showing a configuration example of the analog / digital conversion apparatus 1 in the present concrete example, and like FIG. 3, the analog / digital conversion circuit 2 is shown.
At the same time that the temperature sensor 8 is provided in the control means 3, the environmental temperature is divided into several ranges in the control means 3, and the value of the correction value (α) which is the conversion error used in each temperature range is displayed. Look-up table 9 to identify and store each
And a correction value (α) which is a predetermined conversion error is selected from the look-up table 9 based on the temperature information of the temperature sensor of the analog / digital conversion circuit 2. As in each of the specific examples, the digital conversion output value is corrected.

In addition, in the third specific example, as described above, the specific correction value is adopted in each temperature range as described above, while the entire temperature range is set to a predetermined bit. The resolution may be set based on the number and the degree of the resolution may be used as the conversion correction value. FIG. 7 is a view for explaining the flow chart of the conversion operation in the third concrete example, that is, after the start, in step (1), the environmental temperature of the analog / digital conversion circuit 2 is measured. , The temperature information Ta is transmitted to the control means 3, and in the control means 3, in step (2), it is determined from what temperature area Ta the current temperature belongs. First, the current temperature Ta is judged.
Is less than 25 ° C., and if YES, the process proceeds to step (3), and it is determined whether the temperature Ta is higher than −10 ° C., and if YES, step (4). Proceed to, look up table 9 to -10 ℃
Select the correction value (α) corresponding to the conversion error in the temperature range of from + 25 ° C to correct the digital conversion value, or
As the correction value, 0LSB represented by the resolution may be adopted to perform the correction.

Next, if NO at step (2), the process proceeds to step (5) to look up table 9
From, the correction value (α ′) corresponding to the conversion error in the temperature range of + 25 ° C. or higher is selected to correct the digital conversion value, or the correction value is represented by the resolution −1LS.
The correction may be performed by using B. If NO in step (3), the process proceeds to step (6), in which the correction value (α ″) corresponding to the conversion error in the temperature range of −10 ° C. or less is obtained from the lookup table 9. Select and correct the digital conversion value, or as the correction value,
The digital conversion value is corrected by adopting + 1LSB represented by the resolution.

The flowchart showing the procedure of the operation for converting the analog value into the digital value in the third concrete example is basically the same as the flowchart in FIG. 2 as shown in FIG. The difference is that the value of the correction value α changes according to the temperature region to which the measured temperature belongs.
That is, it is assumed that the analog value pm in step (1) is subjected to analog / digital conversion and converted into a digital value called PM in step (2).

Assuming that the digital value PM has a value of 100, in step (3), if the correction value α is 0 as a result of measuring the environmental temperature, the digital value after correction is corrected. The value PM remains 100, but the correction value α
Is −1, the corrected digital value PM is 99.
Becomes FIG. 11 shows a change in the correction value of the third specific example.

Next, a fourth concrete example of the analog / digital converter having the temperature compensation function according to the present invention will be described. That is, in this specific example, the analog / digital conversion circuit 2 is provided with the reference voltage input terminal 10, and the control circuit 3 calculates a correction value from the converted value of the input reference voltage and the reference voltage. However, it further has a function of correcting the signal output from the output of the analog / digital conversion circuit 2 by using the correction value.

That is, FIG. 9 is a diagram for explaining a configuration example of the analog / digital conversion circuit in the case of executing the present concrete example, and the analog / digital conversion circuit 2 and the appropriate control means 3 are shown.
In the analog / digital conversion device 1 configured from, the reference voltage input terminal unit 10 is provided, which is connected to the analog / digital conversion circuit 2. As the reference voltage input terminal 10, for example, + 5V can be used as a high potential power source and 0V (GND) can be used as a low potential power source. In the fourth specific example of the present invention,
A voltage value obtained by further dividing the reference voltage may be adopted as the reference value.

As an example of such partial pressure, as shown in FIG.
Reference voltage terminal 11 resistance-divided using two resistors R having the same resistance value between the high-potential power source and the low-potential power source.
May be used. In this case, 2.500V is used as the reference voltage value. In this specific example, the reference voltage value is used to calculate the conversion error (α) based on the temperature characteristic of the analog / digital conversion circuit 2, and one of the specific examples is used. Is to set a unit resolution for each bit by dividing the maximum range of the reference voltage into a predetermined number of bits and applying a predetermined potential to each bit.

That is, if the maximum range of the reference voltage is 5V and the range is composed of 10 bits, each bit has a resolution of 4.88V. Therefore, regarding the analog / digital converter, the required standard is ± 2 LSB.
Then, it means that within the compensation temperature range, the analog / digital conversion circuit 2 must have a characteristic that the conversion error is within ± 10 mV.

Therefore, in this specific example, the conversion error (α) due to the temperature at the time of conversion of the analog / digital conversion circuit 2 concerned.
In order to compensate for the above, the reference voltage and the voltage value of the reference voltage after being converted by the analog / digital conversion circuit 2 are compared to obtain the difference, and the difference is calculated by the analog / digital conversion circuit. It is determined that the conversion error (α) is formed based on the influence of the temperature when the conversion process in 2 is executed.

Then, a specific correction value is obtained from the conversion error (α) by the resolution represented by the number of bits, and the correction process is executed. For example, it is assumed that the resolution of a certain analog / digital conversion circuit 2 is 8 bits, and in the analog / digital conversion circuit 2, the voltage of the input channel converted and designated by the control means 3 is
If it is the same as the reference voltage + Vref, the converted value is
If it is displayed in hexadecimal notation, it becomes HEX "FF", and if the voltage of the input channel designated for conversion is the same as the reference voltage -Vref, the converted value is displayed in hexadecimal notation and HEX ". 00 ".

Further, the voltage of the input channel is (+ Vre
f) + (-Vref) / 2, the converted value is HEX
It is expressed as "7F". Therefore, a certain input channel CHn
Is used as a reference voltage value input channel, and the potential difference is divided into two as described above in order to prevent the reference voltage from changing due to temperature, the value is VCHn = (+ Vref) +
(-Vref) / 2, and the voltage value is input.

As a result, the ideal analog / digital conversion value of the input channel CHn becomes HEX "7F".
Here, for example, when the actual analog / digital conversion value of CHn shifts to HEX “7D” due to temperature, the difference between the ideal value and the A / D conversion value, that is, (HEX
“7D”) − (HEX “7F”) = HEX “−02” is adopted as the temperature correction value, and arithmetic processing such as addition or subtraction is performed on the A / D conversion value for other analog input values to change the temperature. This is to compensate the conversion error (α) in the A / D conversion.

Therefore, in this embodiment, the conversion error (α) of the analog / digital conversion circuit 2 due to the influence of the temperature is corrected in real time to the signal output from the output of the analog / digital conversion circuit. It is possible to call.

[0039]

In the analog / digital converter having the temperature compensation function according to the present invention, since the above-mentioned configuration is adopted, the temperature can be controlled by using the simple circuit configuration and the predetermined arithmetic processing. The present invention provides an analog / digital conversion device having a temperature compensation function that suppresses an A / D conversion error due to a change to an ideal value, does not malfunction, and can be manufactured at low cost.

Further, in the circuit according to the present invention, it is possible to obtain an analog / digital conversion device having a temperature compensation function which absorbs a conversion error in the analog / digital conversion circuit due to temperature and stabilizes the control performance. Is possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a configuration in a specific example of an analog / digital conversion device having a temperature compensation function according to the present invention.

FIG. 2 is a flowchart in a first concrete example according to the present invention.

FIG. 3 is a block diagram showing a configuration example of a second specific example according to the present invention.

FIG. 4 is a block diagram showing another example of the configuration of the second specific example according to the present invention.

FIG. 5 is a block diagram showing another example of the configuration of the second specific example according to the present invention.

FIG. 6 is a block diagram showing a configuration example of a third specific example according to the present invention.

FIG. 7 is a flowchart in a third specific example according to the present invention.

FIG. 8 is another flowchart in the third example according to the present invention.

FIG. 9 is a block diagram showing a configuration example of a fourth specific example according to the present invention.

FIG. 10 is a diagram illustrating a relationship between a temperature range and a conversion error in the analog / digital conversion circuit.

FIG. 11 is a diagram illustrating a relationship between a temperature range and a conversion error in the analog / digital conversion circuit according to the third example of the present invention.

FIG. 12 is a diagram illustrating a relationship between an analog input voltage and a digital output voltage.

FIG. 13 is a diagram illustrating a relationship between an ideal conversion value and a conversion error in an analog / digital conversion circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Analog / digital converter having a temperature compensation function 2 ... Analog / digital converter 3 ... Control means, CPU 4 ... Substrate 5 ... Temperature sensor 6 ... Thermistor 7 ... Diode 8 ... Temperature detecting means 9 ... Look-up table 10 ... Reference voltage input terminal 11 ... Divided reference voltage input terminal

Claims (7)

[Claims] 1. An analog / digital conversion device comprising an analog / digital conversion circuit having at least an input / output terminal and a control means for controlling the analog / digital conversion circuit, wherein the control means includes the analog / digital converter. The analog signal input to the input terminal of the digital conversion circuit has a function of performing output correction by adding a predetermined correction value to the digital signal converted and output by the analog / digital conversion circuit. An analog / digital converter having a characteristic temperature compensation function. 2. The analog / digital conversion device according to claim 1, wherein the predetermined correction value is a fixed value determined based on a temperature characteristic peculiar to the analog / digital conversion circuit. . 3. The predetermined correction value is a value represented as a function of a temperature change determined based on an inherent temperature characteristic of the analog / digital conversion circuit. The described analog / digital converter. 4. The predetermined correction value is a fixed value determined based on the inherent temperature characteristic of the analog / digital conversion circuit, and the ambient temperature deviates from a predetermined temperature range. The analog / digital conversion device according to claim 2, wherein the output correction is performed using the correction value in such a case. 5. The analog / digital conversion circuit is provided with a reference voltage input terminal, and the control circuit calculates a correction value from the conversion value of the input reference voltage and the reference voltage, and the correction value. 2. The analog / digital conversion device according to claim 1, further comprising a function of correcting the signal output from the output of the analog / digital conversion circuit by using. 6. The reference voltage input to the analog / digital conversion circuit is further divided at a predetermined ratio,
The analog / digital conversion device according to claim 5, wherein the correction value is calculated using the divided reference voltage. 7. A real-time output from the output of the analog / digital conversion circuit using a conversion value of the input reference voltage or a correction value calculated from the divided voltage value thereof, which includes the element of the change of the environmental temperature. 7. The analog / digital conversion device according to claim 5, wherein the signal to be converted is corrected.